Global environmental and economic concerns regarding increasing fuel consumption and greenhouse gas emission, the rising cost of energy worldwide, and demands for lower operating cost, are driving changes to legislative regulations and consumer demand. As these regulations and requirements become more stringent, advanced engine technologies must be developed and implemented to realize desired benefits.
FIG. 1B illustrates several valve train arrangements in use today. In both Type I (21) and Type II (22), arrangements, a cam shaft with one or more valve actuating lobes 30 is located above an engine valve 29 (overhead cam). In a Type I (21) valvetrain, the overhead cam lobe 30 directly drives the valve through a hydraulic lash adjuster (HLA) 812. In a Type II (22) valve train, an overhead cam lobe 30 drives a rocker arm 25, and the first end of the rocker arm pivots over an HLA 812, while the second end actuates the valve 29.
In Type III (23), the first end of the rocker arm 28 rides on and is positioned above a cam lobe 30 while the second end of the rocker arm 28 actuates the valve 29. As the cam lobe 30 rotates, the rocker arm pivots about a fixed shaft 31. An HLA 812 can be implemented between the valve 29 tip and the rocker arm 28.
In Type V (24), the cam lobe 30 indirectly drives the first end of the rocker arm 26 with a push rod 27. An HLA 812 is shown implemented between the cam lobe 30 and the push rod 27. The second end of the rocker arm 26 actuates the valve 29. As the cam lobe 30 rotates, the rocker arm pivots about a fixed shaft 31.
As FIG. 1A also illustrates, industry projections for Type II (22) valve trains in automotive engines, shown as a percentage of the overall market, are predicted to be the most common configuration produced by 2019.
Technologies focused on Type II (22) valve trains, that improve the overall efficiency of the gasoline engine by reducing friction, pumping, and thermal losses are being introduced to make the best use of the fuel within the engine. Some of these variable valve actuation (VVA) technologies have been introduced and documented.
A VVA device may be a variable valve lift (VVL) system, a cylinder deactivation (CDA) system such as that described U.S. patent application Ser. No. 13/532,777, filed Jun. 25, 2012 “Single Lobe Deactivating Rocker Arm” hereby incorporated by reference in its entirety, or other valve actuation system. As noted, these mechanisms are developed to improve performance, fuel economy, and/or reduce emissions of the engine. Several types of the VVA rocker arm assemblies include an inner rocker arm within an outer rocker arm that are biased together with torsion springs. A latch, when in the latched position causes both the inner and outer rocker arms to move as a single unit. When unlatched, the rocker arms are allowed to move independent of each other.
Switching rocker arms allow for control of valve actuation by alternating between latched and unlatched states, usually involving the inner arm and outer arm, as described above. In some circumstances, these arms engage different cam lobes, such as low-lift lobes, high-lift lobes, and no-lift lobes. Mechanisms are required for switching rocker arm modes in a manner suited for operation of internal combustion engines.
Rocker arms that are driven by a camshaft to actuate the cylinder intake and exhaust valves are typically mounted on the cylinder head.
There are structures extending from the cylinder head such as cam towers to secure and support the camshafts in an overhead cam design. There are also spark plug tubes that extend upward from the top of each cylinder through the head to receive spark plugs. There may be other structures that extend from the cylinder head that support elements of the valve train.
As described above, some embodiments of VVA switching rocker arm assemblies include a rocker arm within a rocker arm that are biased together with a spring on either side. Since the inner/outer arm design often employs a roller in the center to engage a cam lobe, it is advantageous to keep the roller the same width of the cam lobe. Therefore, the structures on either side of the roller add width to the rocker assembly causing it to be wider than original non-VVA rocker arms and too wide to fit certain cylinder head designs.
For example, some Type II engine heads employ cam towers that have a hydraulic lifter adjuster (HLA) near the centerline of the head and spark plug tubes that obstruct one side of a wide VVA switching rocker arm assembly.
Many engine parts are designed by manufacturers to work with a specific cylinder head, making the cylinder head very difficult to modify because changes may impact many interrelated components, possibly increasing cost and causing assembly clearance issues. In some cases, VVA switching systems do not fit in the space defined by the existing head design.
One example of VVA technology used to alter operation and improve fuel economy in Type II gasoline engines is discrete variable valve lift (DVVL), also sometimes referred to as a DVVL switching rocker arm. DVVL works by limiting engine cylinder intake air flow with an engine valve that uses discrete valve lift states versus standard “part throttling”. A second example is cylinder deactivation (CDA). Fuel economy can be improved by using CDA at partial load conditions in order to operate select combustion cylinders at higher loads while turning off other cylinders.
The United States Environmental Protection Agency (EPA) showed a 4% improvement in fuel economy when using DVVL applied to various passenger car engines. An earlier report, sponsored by the United States Department of Energy lists the benefit of DVVL at 4.5% fuel economy improvement. Since automobiles spend most of their life at “part throttle” during normal cruising operation, a substantial fuel economy improvement can be realized when these throttling losses are minimized. For CDA, studies show a fuel economy gain, after considering the minor loss due to the deactivated cylinders, ranging between 2 and 14%. Currently, there is a need for VVA rocker arms for increased performance, economy and/or reduced emissions that fit specific engine head designs.
Switching rocker arms have been used to alter the operation and performance of the engines. For example, specialized rocker arms may be used that provide variable valve actuation (VVA), such as variable valve lift (VVL), and cylinder deactivation (CDA). U.S. Provisional Patent Application No. 61/636,277 describes in detail the structure and function of a VVL switching rocker arm, and the reader is referred to this document for a full description. These have been developed that improve performance, fuel economy, and/or reduce emissions of the engine. Several types of the VVA rocker arm assemblies include an inner rocker arm within an outer rocker arm that are biased together with torsion springs. A latch, when in the latched position causes both the inner and outer rocker arms to move as a single unit. When unlatched, the rocker arms are allowed to move independent of each other. The latch of the inner arm rests on a latch seat of the outer arm. (Alternatively, the latch may be on the outer arm.)
In the past is was thought that in order to utilize a round rocker arm latch you would need the mating surface of the other rocker arm in the assembly to have a ground in curved mating surface. This mating surface can be referred to as a latch seat.
This latch seat would need to have a radius that very closely matches the latch radius. A seat that is slightly too small causes sticking, and a delayed release. It also causes the latch to impact the corners of the latch seat during engagement of the latch. A larger seat or smaller seat could cause undesirable wear.
Due to the tolerances, it would need to be processed by way of grinding. This would require more exact and expensive manufacturing processes. Also, the latch should not be restricting from properly extending and retracting.
Another latch design included creating a number of latches, measuring each and sorting them by latch width. The proper latch was selected having a specific shelf height from an assortment of latches with varying shelf heights to result in a proper lash. This was time-consuming and required an array of parts.
As indicated above, at least some VVA rocker arm assemblies are wider than conventional rocker arms. The increased width tends to interfere with the spark plug tubes, cam towers and other structures of the head. Without modifications, the VVA rocker arm assemblies may not fit existing head designs, and cannot be used. Changes may be required to be made to the head design to accommodate the VVA rocker arm assemblies. However, large changes to the head design may affect parts manufactured by other manufacturers that interface with the head. Therefore, it would be beneficial to provide a head that has small modifications that would allow use of the VVA rocker arm assemblies.
Currently, there is a need for a head arrangement that can accommodate a VVA system while still being compatible with other equipment that interfaces with the head.